1. Field of the Invention
The present invention relates to an efficient resource management method for supporting coverage area expansion of a compact cell without changing 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) Release 8/9 standards. More particularly, the present invention relates to a method for supporting handover between a macrocell and a compact cell to minimize interference received from a macro base station to a terminal communicating with a compact base station within a coverage area of an expanded compact cell when the coverage area of the compact cell is expanded in a heterogeneous network system.
2. Description of the Related Art
Since the demand for high-speed data service continues to increase and the high-speed data service is provided through small coverage areas, a compact cell is drawing much attention. The compact cell is a small cell coverage area formed by a compact base station for accessing a mobile communication core network over a broadband network installed indoors such as an office or a house.
Meanwhile, the 3rd Generation Partnership Project (3GPP) Radio Access Network (RAN) WorkingGroup (WG)1 is working on a Heterogeneous Network (HetNet). The HetNet indicates cellular deployment by overlaying compact cells of a smaller coverage area and a smaller power than a macrocell with the macrocell. That is, the cells of different sizes are mixed or overlaid in the HetNet. Yet, all of the cells in the HetNet adopt the same radio transmission technology. Herein, the compact base station can include a pico base station, a femto base station, a micro base station, a relay node, and a Radio Resource Head (RRH).
In general, the pico base station in the HetNet installs an antenna at a lower elevation than the macro base station. As a result, the installation of the pico base station interrupts the smooth macro offload. That is, although the pico base station is installed in the macrocell, the unequal transmit power between the macro base station and the pico base station degrades a cell splitting gain and a load balancing effect between the macrocell and the picocell. For example, in a 3GPP Long Term Evolution (LTE) system, a terminal selects a cell of the greatest Reference Signal Received Power (RSRP) value as its serving cell based on a downlink RSRP, and selects the macrocell using more transmit power than the picocell.
To address this drawback, the 3GPP Release 10 recently considers a technique for expanding the coverage area of the picocell. The picocell coverage area expansion technique expands the coverage area of the picocell by setting a relatively large bias value for the RSRP value of the picocell, and thus the macro offload is achieved and the capacity can be enhanced by installing the pico base station. That is, the picocell coverage area expansion technique can increase the number of users accessing the picocell by changing the serving cell selection criterion of the terminal, and attain the cell splitting gain and the load balancing effect between the macrocell and the picocell by installing the pico base station in the macrocell.
However, the picocell coverage area expansion is subject to the following problems. When the picocell coverage area is expanded, a terminal which communicates with the pico base station in the expanded coverage area receives severe interference from the macro base station and thus cannot smoothly communicate with the pico base station. Specifically, the terminal communicating with the pico base station cannot normally receive a downlink control signal from the pico base station because of the interference from the macro base station.
Thus, when the picocell coverage area is expanded in the HetNet system, what is needed is an efficient resource management method for minimizing the interference received at the terminal communicating with the pico base station from the macro base station within the expanded picocell coverage area.